Cooled low noise, high frequency transistor



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. W11, HIB BY 6?/ W F IC.3. 'rroxNEYs 3,009,085 4 COOLED LOW NOISE, HIGH FREQUENCY TRANSISTOR Richard L Petritz, Dallas, Tex., assignor to the United States of America s represented by the Secretary of the Navy Filed Nov. 19, 1959, Ser. No'. 854,211

6 Claims. (ci. 317-235) y (Grted llder Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

' This invention relates to an electronicamplifying device capable of operation at very high frequencies up to 100,000 megacycles and more particularly to a transistor capable of operation at very high frequencies up to l100,000 megacycles yand at noise temperatures of 4 K. te 100 K.

At present there are no vacuum tubes which operate at such high frequencies with such low noise temperatures. There are no other transistors at present which operate at such high frequencies. Present germanium transistors operate only to about 1000 megacycle's. Vacuunt-tubs such as travel-ing wave tubes operate at microwave fequencies but -at a'high noise level. The traveling wave tubes are also bulky and require yhigh power iu their operation. 'Maser type amplifiers and parametric amplifiers may be promising approaches to low noise, high frequency amplification. However, generally, these -req'uivre high frequency pumping power of lquite high level. The transistor ofthe `present inventionrequires only conventional D.-C.- power and cooling for its operation. If presenttype transistors of germanium and silicon were cooled to a temperature in the regionof 4 K. to 100 K. theywuld not perform well because of mobility 'reduction, carrier freeze out, and reduced lifetime.

However, as more clearly shown hereinafter, cooling transistors made of indium antimonide to a temperature in the range 4 K. to 100 K. will result in new and unexpected increase in the high-frequency capability and in the low noise performance of the cooled transistor. In

the case of indium arsenide the temperature range is 4 K. to 220 K.

According. to this invention a cooled transistor of a high mobility material such as indium antimonide or indium-arsenside is employed as a solution -to the problem of low noise, very high frequency amplification.

It is an object of this invention toprovide an electronic l device for very high frequency, low temperature amplifica'tion with low noise level.

It is another object of this invention to provide a low noise, veryhigh frequency transistor operable at low temperature. Another object of this invention is to provide a very high frequency, low noise transistor employing a high mobility semiconductor materialv such as indium antimonide orl indium arsenside.

A fui-ther object of this invention is to provide a very high frequency, low noise transistor suitable for operation at temperature from 4 K. to 100 K. A still further object is to provide a transistor lhaving a low noise characteristic.

Another object of this invention is to provide a transistor operable at very high frequencies up to 100,000 megacycles.

Other objects and many of the' attendant advantages of this invention will be readily appreciated as the same better understoodby reference to the following detailed description when considered in connection with the accompanying drawing in which:

3,000,085 Patented nov. 14., 19er icc 2 FIG. 1 illustrates an equivalent circuit for a P-N-P type transistor;

FIG. 2 illustrates a P-N-P type transistor; PIG. 3 villustrates a transistor located within a cooling unit; and y FIG. 4 is a view of another form of an N-P-N type transistor suitable for use 'with the present invention.

Referring now to FIG. 1, illustrating an equivalent transistor circuit of the P-N-P type, the emitter noise Gr1.2i=2q1. 1) where q isthe charge of each chargecarrie'r and Ie is the emitter current. This equation is Valso expressible in terms of the temperature and conductance of the emitter. This relationship comes from Ie=I[eqVe/kTlLlseqVe/kTe for qVe/kTe 1 l., 1 G V kT.,I Glle2l=2qle= 2k Te'Ge (2) From Equation 2 it followsthat cooling the emitter will reduce the noise for a given emitter conductance Ge.

` When the transmitter is connected to an antenna of matched impedance, rg=re=l/Ge, the noise figure can be shown to be,

if the noise from the base resistance and other sources of noise such `as. l/ f noise is neglected. If the effective antenna temperature is low, e.g. T8=4 K. and the transistor is operated 'at room temperature, i.e. 300 K. the transistor will have a poor noise figure However, if the transistor is cooled to 4 K., the noise figure [n.f.=l-|-1/2] will be significantly improved.

types of` transistors such as an N-P-N Mesa type shown in FIG. 4 could be used.

The impurities used for N-type dopingof the semiconductor are materials from group VI of the periodic table such as seleniumv and tellurium. The corresponding P-type doping materials are from group ll of the periodic table such as zinc and cadmium.

Referring to FIG. 3 of the drawing, transistor or semiconductor body lil is shown inside of a refrigerator or cooling unit 13. Cooling unit 13 is equipped with a temperature gan-ge 15 having pointer 17 and dial 19. Any type of cooling unit including Peltier cooling may be used that is capable of maintaining the transistor within a temperature range between 4 K. and 100 K.

'Current flow in a semiconductor can occur by drift of the 'carriers' in the presence of an electric field, or by [referred to. herein as Drift transistors].

by a non-uniform distribution of donor [or acceptor] atoms. Low temperature operation is applicable for both the Diffusion type transistor and the Drift type transistor. Low temperature Diffusion transistors of indium antimonide and indium tarsenside should be feasible and should have llow noise and medium frequency cha-racteristics. The most serious limitation of the low temperature Diffusion transistor is that its high frequencyrespouse -is limited by the fact that carriers must diffuse across the base region. With decreasing temperature the transit time increases and the cut olf frequency decreases.

Drift type transistors are also feasible for low temperature operation. In addition to the low noise characteristic of the Diffusion type, the Drift transistor structure should have unexpected high frequency capabilities in the 10,000 to 100,000 megacycle region. This is achieved through use of InSb when this material is cooled to they temperature range of 4 K. to 100 K.

In the case of the Drift transistor, the cooling to tern-` peratures in the range of 4 K. to 100 K. does not decrease the frequency response in the case of the Diffusion transistor, but on the contrary, causes a substantial increase in the frequency response characteristics of the cooled Drift transistor when made from indium antimonide. For indium -arenside a temperature range of 4 K. to 220 K. is satisfactory.

Applications in which cooling of transistors should be useful include long range radar and communications systems, computers and complex electronic gear in general where high frequency and low noise performance are necessary. The improved noise gures of long range radar and communications systems will provide for lower transmitter power which will result'in a significant decrease in the overall sizeof the equipment. The extra cost of cooling such equipment will be offset yby the reduction in the cost, size and power requirements of the transmitting equipment. In the case of computers, the use of cooling will provide for solving problems with much less equipment.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

t 1. A low noise, very high frequency transistor having an emitter, a base and a collector, and adapted to be operated in a temperature range between 4 K. and 100 K. comprising a semiconductor body composed of indium antimonide semiconductor material, cooling means surrounding said semiconductor body for maintaining said semiconductor body within said temperature range such that `a low noise gure and a high frequency cutoff of l said transistor are produced. I

2. A transistor having a very high-frequency response and a low noise characteristic comprising a semiconductor body composed of an indium antimonide semiconductor material, and cooling means surrounding said semiconductor body for maintaining said body at an operating temperature range between 4 K. rand 100 K. such that a very high frequency cutotf and a low noise figure of said transistor may be attained.

3. A low noise, very high frequency transistor adapted to be operated in a temperature range between 4 K. and 220 K. comprising a semiconductor body composed of an indium arsenide semiconductor material; cooling means surrounding said semiconductor body to maintain said semiconductor body within said temperature range such that a very high frequency cutoff and a low noise figure are produced.

4. A transistor having a very high frequency response and a low noise characteristic comprising a semiconductor body composed of indium arsenide semiconductor material, and means surrounding said semiconductor body for maintaining said body at an operating temperature range between 4 K. and 220 K. to increase the frequency cutoff and reduce the noise figure of said transistor whereby said high frequency response and said low noise characteristics are made possible.

5. A low noise, very high frequency transistor having an emitter, a base and la collector, and adapted to be operated in the temperature range between 4 K. and 220 K. comprising a semiconductor body composed of a semiconductor material selected from the class consisting of indium arsenide and indium antimonide; means surrounding said transistor for maintaining said temperature range to increase the cutoff frequency and reduce the noise figure of said transistor such that said transistor may be operated at very high frequencies and at low noise conditions.

6. A transistor having a very high frequency response References Cited in the tile of this patent UNITED STATES PATENTS 2,796,563 Ebers et al. June 18, 1957 2,798,989

Welker July 9, 1957 

